Intra-aortic balloons are designed to assist a failing heart through cyclic inflation/deflation in the descending thoracic aorta, in counterpulsation to the heart. Such balloons are generally inserted percutaneously into the femoral artery and advanced along the arterial path to the descending thoracic aorta. Intra-aortic balloons consisting of a catheter with two coaxial tubular members defining two lumens, are known, for example, as shown in U.S. Pat. No. 4,540,404 to Wolvek. An outer tubular member (outer lumen) is included, being substantially circumferentially rigid but longitudinally flexible, having its distal end attached to the proximal end of an inflatable balloon. An inner tubular member (inner lumen) is coaxially disposed in the outer tubular member, and is similarly longitudinally flexible, having its distal end attached to the balloon distal end. The inner tubular member supports the balloon.
The intra-aortic balloon is wrapped around the inner tubular member for insertion into the artery, with vacuum applied to the balloon interior to assure tight wrapping and the absence of air pockets. Tight, smooth wrapping is essential as a small diameter and smooth balloon outer surface provide less resistance during insertion, and reduce arterial wall contact during travel through the artery.
Intra-aortic balloon assemblies of this type usually utilize a guide wire which is inserted through an incision into the common femoral artery, such as by using the standard Seldinger technique. The guide wire is thin and readily guidable through the artery. Once the wire is positioned, the inner tubular member of the balloon assembly is passed over the wire until the balloon reaches the desired location. The balloon is then unwrapped, connected to its pumping apparatus and counterpulsation initiated.
While a guide wire can be directed through delicate, tortuous and narrow vasculature, it is often difficult to advance the balloon assembly over the guide wire for any great distance. If the inner tubular member is relatively rigid in its longitudinal duration, it may not track properly over the wire because advancement of the assembly will buckle the wire in a narrow turn, pulling the guide wire out of the distal vessel and posing a possible risk of penetration of the vessel wall by the relatively rigid member. On the other hand, catheters having a soft, longitudinally flexible inner tubular member, such as that disclosed in U.S. Pat. No. 4,402,307, have no difficulty in following the wire. However, some practitioners may prefer the stiff feel provided by a rigid inner lumen.
One arrangement for providing better guidability to a relatively rigid balloon catheter is shown in U.S. Pat. No. 4,362,150 to Lombardi, Jr. et al.. A metallic inner tubular member is used which does not extend for the entire length of the balloon, with the member being bendable but relatively rigid in its axial direction. The balloon distal end is fixed to an inwardly projecting segment of a longitudinally flexible outer tubular member. The metallic inner tubular member is coaxial with the flexible tubing within the balloon membrane. This provides some flexibility to the forward part of the balloon. However, since the flexible tubing extends into the balloon membrane, it is only marginally effective in providing sufficient flexibility for balloon guidance. Also, insertion and travel of the balloon along a tortuous path concentrates bending stresses at the flexible tube/rigid tube juncture within the balloon, which may weaken the juncture, causing separation and balloon failure. In addition, the enlarged cross-section of the tube juncture within the balloon membrane retards the tightness of the wrap, and creates a larger wrapped diameter, limiting the ease of insertion of the assembly into the femoral artery.
In U.S. Pat. No. 4,739,768 to Engelson, a noncoaxial, single lumen catheter for use with a guide wire is disclosed which includes a relatively stiff proximal segment and a relatively flexible distal segment. The tubular member has a flexible distal extension for leading the relatively stiff inner tubular member along a tortuous path. However, the catheter of Engelson is not a balloon catheter, rather being designed to deliver fluids to a particular target site.